The invention relates to a drafting device for spinning-knitting machines with a drafting arrangement, with which at least two roving yarns can be drawn parallel to form fibre strands and at the outlet of which a nozzle unit with twist nozzles arranged parallel to one another for each of the drawn fibre strands is arranged.
Such drafting devices are known from document WO 2009/026734 A1, for example. They serve to feed fibre strands produced from a roving yarn with substantially parallel oriented fibres to the knitting needles of a knitting machine. The knitted fabrics produced from such fibre strands have a clearly softer surface compared to the surface of knitted fabrics produced from conventional yarns. Since the space conditions particularly on circular knitting machines are confined, at least two fibre strands are drawn parallel to one another with the drafting devices, are provided with a false twist by means of twist nozzles and then fed to knitting needles of adjacent knitting points. For this, the nozzle unit connected to a vacuum unit has a twist nozzle for each of the fibre strands generated by the drafting arrangement.
In the known drafting units malfunctions often occur when fibres of a fibre strand are also drawn in by the adjacent nozzle. This problem mainly arises when the nozzle associated with the fibre strand is blocked.
A ring spinner is known from DE 195 00 036 A1, which has a continuous perforated roller as bottom roller and two top rollers interacting with the perforated roller for parallel drawing of two fibre strands. In the event of a thread break both fibre strands are aspirated off by a common suction tube. An unfavourable influence on the two yarns formed in parallel as a result of transverse fibres of the respective other yarn is prevented by a separator plate, which is arranged at the mouth of the suction tube and extends up to the location of the perforated roller, at which the two formed yarns are removed from the perforated roller. However, the yarns are not transported further by the suction tube here, but are pulled free from the perforated roller. The suction tube merely serves to remove the yarns in the event of a thread break, wherein a suction tube is provided for both yarns.